A hard-disk drive (HDD) is a non-volatile storage device that is housed in a protective enclosure and stores digitally encoded data on one or more circular disks having magnetic surfaces. Historically, when an HDD is in operation, each magnetic-recording disk is rapidly rotated by a spindle motor system. Data is read from and written to a magnetic-recording disk using a read/write head transducer (also referred to as a “read/write head” or simply “head”) which is positioned over a specific location of a disk by an actuator.
A read/write head uses a magnetic field to read data from and write data to the surface of a magnetic-recording disk. As a magnetic dipole field decreases rapidly with distance from a magnetic pole, the distance between a read/write head, which is housed in a slider, and the surface of a magnetic-recording disk must be tightly controlled. Suspensions have a spring-like quality which biases or urges the air bearing surface (ABS) of the slider against the disk to enable the creation of the air bearing film between the slider and disk surface. An actuator relies in part on the suspension's force on the slider and on the aerodynamic characteristics of the slider ABS to provide the proper distance between the read/write head and the surface of the magnetic-recording disk (the “flying height”) while the magnetic-recording disk rotates. A slider therefore is said to “fly” over the surface of the magnetic-recording disk.
As noted, historically HDDs included a spindle motor system, with fluid dynamic bearings (FDB) being a common and important component of such systems. However, use of FDBs within HDDs presents some challenges. For example, FDBs typically provide too little tilt stiffness because the journal bearing span is constrained by the overall HDD thickness, with 5 mm (thick) HDDs being the current trend toward thinner and thinner drives. Current approaches to gaining more tilt stiffness in FDB designs include variations of the FDB groove parameters, such as the depth, land-groove ratio, and clearance. However, what is really needed for FDB designs is FDB axial bearing span, which is becoming more and more at odds with the trend toward thinner HDDs. Additionally, other common problems with the use of FDBs in HDDs include oil loss through evaporation and atomization, oil contamination, cavitation, temperature-sensitive torque, and shock sensitivity (e.g., splashing).